The ideal footwear design would incorporate the following essential features and characteristics: comfort, cushioning, shock absorption, stability, flexibility, support, good fit, and would also be lightweight. These features are achieved in, and are dependent upon, the structural and functional design elements of the footwear, which enhance the wearer's ability to perform various activities without pain or inconvenience.
To date, prior art footwear constructions have failed to successfully combine the essential features of an ideal design. Prior attempts to create the ideal footwear design have been unsuccessful largely because prior structures have emphasized one of the above-noted features to the detriment of others. Furthermore, prior attempts to construct an ideal footwear design have failed to consider the importance of other key features such as industrialized construction, style and fashion.
Prior art footwear constructions which provide cushioning generally have three or four separate parts. First, such conventional footwear designs are provided with an outsole. The outsole is made of a durable material that extends across the lower surface of the shoe and contacts the ground during use to provide traction. The outsole may also have integrally molded full or partial side walls extending upwardly around its periphery. Second, a midsole is permanently joined to the outsole on its interior upper surface and any abutting outsole interior side wall surfaces to provide a cushioning layer within the footwear structure. In some cases the midsole and outsole material are formed as one component of similar or dissimilar materials. Third, an upper, usually formed of leather, synthetics or other materials, is joined to the top surface of the midsole and any abutting interior sidewall surfaces of the outsole and midsole which extend upwardly around the periphery of the upper. Fourth, in many prior art constructions, a thin cushioning insole is further provided for disposal between the top surface of the midsole and the wearer's foot.
The conventional footwear cushioning components and their positioning within the footwear structures of prior art constructions have several undesirable characteristics. For example, it is well known in the art that the cushioning properties of the materials used in footwear midsole and insole designs are substantially reduced after the footwear has been used for a period of time. In some instances, a substantial reduction in cushioning can occur in a relatively short period of time. The footwear midsole and insole components are typically made of various foam and rubber materials which are subjected to repeated application of impact forces and stress which cause compression set, degradation, and fatigue resulting in reduced resiliency and failed cushioning properties. The typical foam midsole and insole cushioning materials are various formulations of sheet stock or molded eva, polyethylene, and polyurethane. The typical rubber materials are latex and neoprene.
The midsoles in prior art footwear constructions that are permanently attached to the footwear also have several undesirable characteristics. For example, the consumer at the point of purchase is unable to make an alternative choice in the cushioning characteristics of the midsole without selecting separate footwear designs. Also, the wearer is unable to replace the midsole component after it has degraded and lost its ability to provide adequate cushioning and support. In addition, the attachment of the midsole to other components in the footwear structure such as the top surface of the outsole, abutting outsole side wall interior surfaces, and to the formed upper negate the ability of the midsole component to adequately compress, deform, and rebound while providing maximum cushioning.
Another undesirable feature of prior art designs is that the ability of the footwear structure to provide maximum cushioning of the foot structures at the appropriate instant in the gait cycle is negated in prior footwear constructions by the positioning of semi-rigid and rigid structural elements in close proximity to the wearer's foot. The semi-rigid and rigid structural elements are typically positioned below the wearer's foot on the top surface of the midsole or slightly recessed into the top surface of the midsole. The typical semi-rigid and rigid structural elements are: shanks, shank stiffeners, lasting insoles, stabilizers, and fasteners. The shanks, shank stiffeners, lasting insoles, stabilizers, and fasteners are usually made of metals, fiber composites, thermoplastics, and fibrous paper board. All of these semi-rigid and rigid structural elements negate the performance and cushioning ability of the midsole, and therefore negatively impact user comfort.
In some footwear constructions a lasting margin structure is formed by the combination of gathered upper materials and the adhesives used to attach the upper to the lasting insole or top surface of the midsole. This lasting margin structure extends around and projects inward from the periphery of the lasting insole or midsole to a distance of approximately 15.0 mm to 25.0 mm creating a semi-rigid border within the footwear structure. This formed structure also negates the performance and cushioning ability of the midsole, to the detriment of user comfort.
Furthermore, midsoles in prior art footwear constructions that are permanently attached to the footwear have external surfaces, especially along the side portions thereof, which are exposed to environmental conditions such as heat, cold, water, ultraviolet rays, abrasion from rocks, sand, soil, punctures from sharp pointed objects, and cuts from sharp edged objects. The environmental conditions contribute to the failure of midsole component cushioning in two main ways: degradation of the midsole cushioning materials, and destruction of the means by which the midsole cushioning component is attached to the footwear structure.
Another undesirable feature of prior art designs is that the thin cushioning insole which is positioned between the top surface of the lasting insole or midsole and the wearer's foot is typically too thin to provide optimal cushioning.
In an attempt to overcome some of the above-described deficiencies of prior art designs, some prior art constructions have incorporated custom or removable midsole inserts. These structures, however, remain encumbered by undesirable characteristics. One such structure is described in U.S. Pat. No. 4,881,328 (hereinafter "the '328 patent") to Lin Yung-Mao. The '328 patent describes a structure with an outsole and a peripheral midsole. A midsole insert is disposed over the peripheral midsole with cushioning elements extending downward adjacent the outsole. Unfortunately, the midsole insert and cushion elements must conform to a matching lift height of the peripheral midsole member. The peripheral midsole member also provides the only method of retaining midsole insert and structural support for the peripheral area of the shoe. The upper must be attached to the top surface of the peripheral midsole member, and the bottom surface of the peripheral member is attached to the upper surface of the outsole. The midsole insert must have an outwardly projecting lip to cover the upper which is attached at the peripheral member. Thus, the method of construction is complex and inefficient, and does not provide for maximum full perimeter cushioning since the rigid peripheral member is in close proximity to the user's foot. The structure also has no means of providing for a midsole insert for a raised heel design typically found in dress, casual shoe, and boot constructions, and fails to provide air circulation within the structure.
Thus, a need exists in the art for an improved footwear structure that provides full perimeter maximum cushioning of the foot structures, support and stability for the foot structures, allows the positioning of semi-rigid and rigid structural elements away from the wearer's foot, and can provide maximum cushioning without the restrictions caused by attachment of the midsole to other components in the footwear structure. Further, a need exists for a removable custom midsole insert that: can be selected according to the wearer's cushioning preference, can be selected according to the wearer's weight, can be selected according to various performance feature options, can provide air circulation within the footwear's interior environment, can be replaced after a substantial reduction and degradation of midsole cushioning occurs and can protect the midsole cushioning element from damage due to environmental conditions.